Method to reduce noxious components in the exhaust of internal combustion engines

ABSTRACT

The ratio of fuel to air of the air-fuel mixture being applied to internal combustion engines is adjusted such that it is below the stoichiometric value; the composition of the exhaust gases from the internal combustion engine is then sensed before they are discharged in the atmosphere, and additional air is introduced to the exhaust gases before their liberation so that a predetermined optimal relationship with respect to the stoichiometric value is obtained.

United States Patent 11 1 Scholl [45}v Sept. 3, 1974 METHOD TO REDUCE NOXIOUS COMPONENTS IN THE EXHAUSTOF INTERNAL COMBUSTION ENGINES [75] Inventor: Friedrich Scholl, Stuttgart, Germany [73] Assignee: Robert Bosch GmbH, Schillerhohe, Germany 22 Filed: July 12, 1972 21] Appl. No.2 271,009

[30] Foreign Application Priority Data Mar. 30, 1972 Germany 2215533 [52] US. Cl 60/274, 60/276, 60/285, 60/289, 23/288 F, 123/119 R, 423/212 [5l]- Int. Cl. F02b 75/10, FOln 3/14 [58] Field of Search 60/274, 285, 276, 289; 23/232 E, 255 E, 288 F; 423/212; 123/119 R [56] References Cited UNITED STATES PATENTS 6/1941 Becker 60/276 5/1962 Barnes 60/276 3,284,165 11 1966 Baumann 23/255 E 3,406,515 10 1968 Behrens 60/274 3,441,381 4/1969 Keith 60 276 3,464,801 9/1969 Barstow 60/276- 3,616,274 10 1971 Eddy.... 60 276 3,683,625 8/1972 McCrink.. 60 276 3,696,618 10/1972 Boyd 60/276 3,730,157 5/1973 GerhOld... 60/285 3,738,341 6 1973 LOOS 3,768,259 10/1973 Camahan 60/276 Primary Examiner-Douglas Hart Attorney, Agent, or FirmFlynn & Frishauf [5 7 ABSTRACT The ratio of fuel to air of the air-fuel mixture being applied to internal combustion engines is adjusted such that it is below the stoichiometric value; the composition of the exhaust gases from the internal combustion engine is then sensed before they are discharged in the atmosphere, and additional air is introduced to the exhaust gases before their liberation so that a predetermined optimal relationship with respect to the stoichiometric value is obtained.

12 Claims, Drawing Figures LAIR ' 7\ 1 CONTROL Fig.1

CONTROL lAIR 18 FUEL I BLOWER AMPL. SENSOR Fig. 2

-METIIOD TO REDUCE NOXIOUS COMPONENTS IN THE EXHAUST OF INTERNAL COMBUSTION ENGINES CROSS REFERENCE TO RELATED PATENT AND APPLICATIONS US. Pat. No. 3,483,851, Reichardt, Dec. 16, 1969 US. Pat. No. 3,745,768, Zechnall et al., July 17,

US. Ser. No. 259,157, filed June 2, 1972, Schmidt et U.S. Pat. No.- 3,759,232, Wahl et al.

US. Ser. No. 259,134, filed June 2, 1972, Topp et al.

US. Pat. No. 3,782,347, Schmidt et al.

US. Ser. No. 267,562, filed May 6, 1972, Eichler et' The present invention relates to a method to reduce noxious components being liberated and exhausted from internal combustion engines and more particularly to such systems which utilize a thermal or a catalytic reactor, or both, in order to treat the exhaust gases from the engines.

Reference in the specification will be made to the air number, denoted lambda (A). This air number A is a measure of the composition of the air-fuel mixture. The

number A- is proportional to the mass of air and fuel, and the value of this number A is one (A 1.0) if a stoichiometric 'mixture is present. Under stoichiometric conditions, the mixture has such a composition that, in view of the chemical reactions, all hydrocarbons in the fuel can theoretically combine with the oxygen in the air to provide complete combustion to carbon dioxide and water. For air and gasoline, the ratio, by weight, for A 1 is about 14.4:1. In actual practice, even with a stoichiometric mixture, unburned hydrocarbons and carbon monoxide are contained in the exhaust gases.

Various methods have been proposed-in which the ratio of the mass of the fuel to air of the air-fuel mixture being applied to internal combustion engines is closely controlled. The mixture is controlled to have a value of A approximately equal to one '(A-='1) Control'of the air number A is obtained by sensing the composition of the exhaust gases from the internal combustion engine, the composition being sensed bysuitable sensors. Such apparatus provide good results. Accurate controlof the air number A, however, requires a comparatively complex apparatus so that control of this air number is so set that the exhaust emission becomes a minimum.

It is an object of the present invention to improveknown methods and systems to control the exhaust emission from internal combustion engines and to provide a method in which the requirements on apparatus for accurate control of the A can be reduced while still maintaining low exhaust emissions.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, the engine is supplied with a rich mixture, that is,one in which (A l The resulting composition of the exhaust gases is sensed .with a sensing device. Depending on the output signal from the sensing device, additional air is introduced to the exhaust gases until the value of A in the exhaust gases has a predetermined level. In accordance with the feature of the invention, a system is provided which is reliable and inexpensive in construction, and carrying out the invention. The system includes an amplifier, which is connected to the sensing device to control a valve which controls the injection of airinto the exhaust system of the internal combustion engine.

The invention will be described by way of example with reference to the accompanying drawings wherein:

FIG. 1 is a schematic block diagram illustrating the system of the present invention and useful in the explanation of the method;

FIG. 2 is a fragmentaryview of a portion of the system, illustrating in modification; and

FIG. 3 is a fragmentary View illustrating a different modification. j

Catalytic or combined thermo-chemical and catalytic reactors to treat and detoxify the exhaust gases of internal combustion engines are particularly applicable with automotive internal combustion engines,-in order to permit operation of the engine with a minimum of polluting exhaust being liberated into the atmosphere. The results of pollution-reducing systems are particularly good when the reactors have gas applied thereto in which the composition is accuratelycontrolled, particularly with respect to the oxygen balance or oxygen level. Such control is best obtained'when the air number A of the fuel-air mixture being applied to the internal combustion is slightly rich, that is, has a composition which is slightly below the stoichiometric value. The air number A should, for example, be A 0.995. At this value, hydrocarbon and carbon monoxide have been sufficiently oxidizedythere are, however, small remainders of carbon monoxide (for example, of about 0.1 percent) to reduce nitrogen-oxygen compounds. Control of the air-fuel ratio applied to the internal combustion engine, that is, applied to its input, requires control apparatus which is relatively expensive and complicated if it is to be accurate to even i 1 percent. In accordance with the invention, the air-fuel mixture which is applied to the internal combustion engine is only roughly determined, for example, by means of car'- buretors, fuel injection pumps or other known devices, the control being set to provide a mixture to the inlet of the internal combustion at an air number A 0.95 to A 0.99, depending on the operating parameters within which'the engine operates or to.which the engine is subjected. This control of the air number of the mixture being supplied tothe engine can be effected in dependence .on engine speed, ambient air pressure, temperature and other parameters. In order to obtain an accurately defined optimum composition of the exhaust gases forsubsequent treatment of the exhaust 3 gases, secondary air is applied to the exhaust gas of the internal combustion engine, the air being applied thereto behind the combustion chambers, 'that' is, for example, to the exhaust manifold of the internal combustionengine. A typical sensing device is an oxygen sensor. Such secondary air, applied to the exhaust syst'em of the internal combustion engine, may be approximately 0.5 percent to 5 percent of the air applied to the input of the engine. The requirements regarding accuracy are thus substantially less since a relative error of about i percent can influence the air number A by at most 0.5 percent. Thus, it is sufficient to provide control of the air-fuel mixture applied to the input of the engine which is matched to the engine'during its operation and to provide for fine control of the composition of the exhaust gases by controlling the secondary air introduced to the exhaust system of the internal combustion engine in order to obtain an accurately defined composition of the exhaust gases themselves. Tolerances of adjustment, and changes in such a control are automatically compensated during the operating time of the internal combustion engine and the associated elements, by controlling the secondary added air.

Referring to the drawings, the internal combustion engine 10 has an air-fuel mixture applied thereto, the air being freely introduced, and fuel being supplied from a fuel tank 11 by means of a well-known metering device 18, for example, acarburetor, a fuel injection system or the like. Metering device 18 is so set that the mixture applied to the engine is slightly rich, that is, the air number A is less than 1. The exhaust from the internal combustion engine is then applied to a catalytic reactor 12. An exhaust gas sensing device 13 is located in the exhaust system, for example, behind the reactor 12, to sense the composition of the exhaust gases. Output signals'are obtained from the sensor 13 which will be representative of the composition of the exhaust gases in-the exhaust system of the internal combustion engine. These signals are applied over an amplifier 14 to control the setting of the control valve 15 which is interposed into an air line 16 connecting a blower 17 to the exhaust system, for example, the exhaust manifold of the internal combustion engine. Opening the valve more or less, introduces more or less in additional air into the exhaust system of the engine. Valve 15 thus can control the amount of additional air being introduced into the exhaust system of the internal combustion engine, so that the air number A of the gases being applied to the reactor 12 can be accurately controlled to a desired value. Air, which is applied over line 16 to the exhaust system of the internal combustion engine is appliedfrom blower 17, which, for example, can be directly driven from the internal combustion engine 10 since with a given A, the secondary air which is required is roughly proportional to engine speed (as a first approximation).

The air sensor 13, as shown in FIG. 1, is connected downstream from catalytic reactor 12. It is also possible to break the exhaust system, for example. the exhaust manifold 19 at points X, X and introduce the sensor 13 upstream-from the reactor 12. This embodiment is illustrated in FlG. 2, where a conventional senthe engine, and the additional air supplied by blower 17 over valve 15 and through line 16. If the sensor is located upstream of junction 20, then only the engine exhaust gases themselves would be sensed and any errors in the control loop between the sensor 13 and the blower 15 would not be detected.

The exhaust manifold 19 of the engine, particularly close to the exhaust valves themselves, can be insulated so that it, itself, will form a thermal reactor for oxidation of carbon monoxide and unburned hydrocarbons, the junction 18 being located adjacent to or within the portion of the exhaust system forming a thermal reactor.

Theoutput signal from sensor 13, amplified in amplifier 14 can also be utilized to control the relative portion of air and fuel being applied to the metering device, for example, by means of a control system 21, to approximately adjust the air number to be just below a value of one.

Sensors suitable in the system and method of the present invention are described in copending cross referenced application Ser. No. 259,134, filed 'June 2,

1972, assigned to the assignee of the present application.

Various changes and modifications may be made within the inventive concept.

I claim: a

1. Method to reduce noxious components in the exhaust of an internal combustion engine in which a reactor means (12) is provided to treat the exhaust gases, and asensing means (13; 23, 33) is exposed to the exhaust gases. and provides anoutput signal representative of the composition of the exhaust gases, said method comprising the steps of sensing the presence, or absence of free oxygen in the exhaust gases from the engine to obtain a measure of the composition of theexhaust gases from the engine before their liberation into the atmosphere;

controlling the proportion of air and fuel (A) of the fuel-air mixture applied to the internal combustion engine to be below the a stoichiometric value of unity l);

introducing additional air into th fore such liberation;

controlling said introduction of additional air to the exhaust gases until the gases have a predetermined optimal relationship with respect to the stoichiofmetric value ()t=1); and further controlling the proportion of air and fuel (A) of the fuel-air mixture applied to the internal combustion engine in dependence on the sensed compositionof the exhaust gases. i

' 2. Exhaust control system for an internal combustion engine comprising 1 means (18) controlling the relative proportion of air and fuel being applied to the engine to provide a mixture of fuel and air always having an air number less than unity ()t l) to the engine;

means (15) controllably introducing air to the exhaust system (19) of the engine, said exhaust system' including a reactor (12);

anoxygen sensing means (13, 23, 33),located to be exposed to the exhaust gases from the engine and sensing for the presence, or absence, of free oxygen in the exhaust gases from the engine;

exhaust gases becontrollable means (17, 16, 15, 18) connected to the exhaust system (19) and further controlled by the output from the sensing means (13, 23, 33) to controllably introduce an amount of air into the exhaust system of the engine which has a predetermined optimal relationship with respect to the stoichiometric value of the exhaust gases; and means (21) controlled by the oxygen sensing means (13, 23, 33) connected to and further controlling said air-fuel proportioning means to control the air-fuel ratio in dependence on sensed composition of the exhaust gases.

3. System according to claim 2, wherein the air introduction means comprises a controllable valve (15) being connected to and controlled by the output from the sensing means (13).

4. System according to claim 3, wherein the air introduction means further comprises a blower applying air under pressure to the controllable valve (15) said blower being driven by the internal combustion engine and having a speed proportional thereto.

5. System according to claim 2, wherein the reactor comprises .a catalytic reactor (12) and the sensing means (13). is connected downstream from the catalytic reactor.

1 6 10. Method according to claim 1, wherein the step of sensing the presence, or absence of free oxygen in the exhaust gases from the engine comprises sensing the exhaust gases which have passed through the reactor (12) downstream from the reactor.

11. Method to reduce noxious components in the exhaust of an internal combustion engine in which a reactormeans (12) is provided to treat the exhaust gases, and asensing means (13; 23, 33) is exposed to the exhaust gases and provides an output signal representative of the composition of the exhaust gases, said method comprising the steps of sensing the presence, or absence of free oxygen in the exhaust gases from the engine to obtain a measure of the composition of the exhaust gases from the engine before theirv liberation into the atmosphere;

controlling, in response to the sensed presence or absence of free oxygen in the exhaust gases, the proportion of air and fuel (A) of the fuel-air mixture applied to the internal combustion engine to have an air number only within the range of A=O.95 to 0.99; introducing additional air into theexhaust gases before such liberation; v I p and controlling, in response to the sensed presence or absence of free oxygen in the exhaust gases, said introduction of additional air to the exhaust gases before such liberation to provide a composition of exhaust gases having an air, number of just under t=l.'0000. 12. Method according to claim 11, wherein the step of sensing the presence, or absence of free oxygen in the exhaust gases from theengine comprises sensing the exhaust gases which havepassed through the reactor (12) downstream from the reactor. 

1. Method to reduce noxious components in the exhaust of an internal combustion engine in which a reactor means (12) is provided to treat the exhaust gases, and a sensing means (13; 23, 33) is exposed to the exhaust gases and provides an output signal representative of the composition of the exhaust gases, said method comprising the steps of sensing the presence, or absence of free oxygen in the exhaust gases from the engine to obtain a measure of the composition of the exhaust gases from the engine before their liberation into the atmosphere; controlling the proportion of air and fuel ( lambda ) of the fuel-air mixture applied to the internal combustion engine to be below the stoichiometric value of unity ( lambda <1); introducing additional air into the exhaust gases before such liberation; controlling said introduction of additional air to the exhaust gases until the gases have a predetermined optimal relationship with respect to the stoichiometric value ( lambda 1); and further controlling the proportion of air and fuel ( lambda ) of the fuel-air mixture applied to the internal combustion engine in dependence on the sensed composition of the exhaust gases.
 2. Exhaust control system for an internal combustion engine comprising means (18) controlling the relative proportion of air and fuel being applied to the engine to provide a mixture of fuel and air always having an air number less than unity ( lambda <1) to the engine; means (15) controllably introducing air to the exhaust system (19) of the engine, said exhaust system including a reactor (12); an oxygen sensing means (13, 23, 33) located to be exposed to the exhaust gases from the engine and sensing for the presence, or absence, of free oxygen in the exhaust gases from the engine; controllable means (17, 16, 15, 18) connected to the exhaust system (19) and further controlled by the output from the sensing means (13, 23, 33) to controllably introduce an amount of air into the exhaust system of the engine which has a predetermined optimal relationship with respect to the stoichiometric value of the exhaust gases; and means (21) controlled by the oxygen sensing means (13, 23, 33) connected to and further controlling said air-fuel proportioning means to control the air-fuel ratio in dependence on sensed composition of the exhaust gases.
 3. System according to claim 2, wherein the air introduction means (15) comprises a controllable valve (15) being connected to and controlled by the output from the sensing means (13).
 4. System according to claim 3, wherein the air introduction means further comprises a blower applying air under pressure to the controllable valve (15) said blower being driven by the internal combustion engine and having a speed proportional thereto.
 5. System according to claim 2, wherein the reactor comprises a catalytic reactor (12) and the sensing means (13) is connected downstream from the catalytic reactor.
 6. System according to claim 2, wherein the reactor comprises a catalytic reactor (12) and the sensing means (23, 33), is connected upstream and ahead of said catalytic reactor.
 7. System according to claim 6, wherein the sensing means (23) has a cataLytically-active surface (23a).
 8. System according to claim 6, wherein the sensing means further comprises catalytic means (33a) in the stream of the exhaust gas to which the sensing means (33) is exposed.
 9. System according to claim 2, wherein the sensing means (13) is connected downstream from the reactor (12).
 10. Method according to claim 1, wherein the step of sensing the presence, or absence of free oxygen in the exhaust gases from the engine comprises sensing the exhaust gases which have passed through the reactor (12) downstream from the reactor.
 11. Method to reduce noxious components in the exhaust of an internal combustion engine in which a reactor means (12) is provided to treat the exhaust gases, and a sensing means (13; 23, 33) is exposed to the exhaust gases and provides an output signal representative of the composition of the exhaust gases, said method comprising the steps of sensing the presence, or absence of free oxygen in the exhaust gases from the engine to obtain a measure of the composition of the exhaust gases from the engine before their liberation into the atmosphere; controlling, in response to the sensed presence or absence of free oxygen in the exhaust gases, the proportion of air and fuel ( lambda ) of the fuel-air mixture applied to the internal combustion engine to have an air number only within the range of lambda 0.95 to 0.99; introducing additional air into the exhaust gases before such liberation; and controlling, in response to the sensed presence or absence of free oxygen in the exhaust gases, said introduction of additional air to the exhaust gases before such liberation to provide a composition of exhaust gases having an air number of just under lambda 1.0000.
 12. Method according to claim 11, wherein the step of sensing the presence, or absence of free oxygen in the exhaust gases from the engine comprises sensing the exhaust gases which have passed through the reactor (12) downstream from the reactor. 